Time domain and digital domain have been regarded as the reliable representations for analog information processing in finer scale geometries. A time-to-digital converter is commonly used in a processing system circuit to convert the time information into the digital representation. The time-to-digital converter is widely applied in thriving areas including digital phase-locked loops (DPLL) for radio frequency (RF) wireless communication systems, the time-based analog-to-digital converter and the time-of-flight (ToF) ultrasonic sensing. Meanwhile, different modules within such a system usually share the power supply, which leads to the consideration of the noise coupling among these modules through the power supply.
Normally, noise shaping time-to-digital converters achieve the noise reduction within the output signal bandwidth by shaping the quantization error through utilizing a controlled oscillator, such as a gated ring oscillator or a switched ring oscillator. However, the in-band output noise is dominated by the phase noise of the oscillator, and previously there is no technique to reduce the impact from such phase noise. Moreover, the oscillator is sensitive to the power noise, and the oscillator introduces their operation noise to the power supply at the same time. Thus, for protecting other modules from disturbance, an extra power supply separated from other modules is needed for the time-to-digital converter based on the oscillator in a higher-level system, which is disadvantageous in terms of the overall system design.
Therefore, there is a need of providing a time-to-digital converter to obviate the drawbacks encountered from the prior arts.